1. Field of the Invention
This invention relates to a method of calibrating or checking the accuracy of a pressure gauge and more specifically to a method and apparatus for calibrating or checking the accuracy of a sphygmomanometer pressure gauge.
2. Description of Prior Art
A sphygmomanometer is a device used by physicians and medical personnel to measure the blood pressure of a patient. Sphygmomanometers were previously constructed so as to have a mercury column which was used to measure the blood pressure. Sphygmomanometers must be accurate since medical personnel prescribe treatments and/or medication on the basis of a patient's blood pressure and even a minor error or inaccuracy in the indicated blood pressure may result in harm to the patient. The mercury column-sphygmomanometer was easily checked for accuracy by adjusting the zero level of the mercury column, as by changing the amount of mercury in the reservoir when no pressure was supplied. With advancements in the art of sphygmomanometers, the mercury column was abandoned in favor of a more compact pressure gauge operated by means of a bellows mechanism to measure blood pressure. However, such pressure gauge-sphygmomanometers are sensitive to mechanical abuse and must be regularly checked for accuracy.
The present method of calibrating or checking the accuracy of a sphygmomanometer pressure gauge consists of removing the pressure gauge from the sphygmomanometer device and securing it to an upper leg of a Y-tube, the other upper leg being connected to a column of mercury and the lower leg of the tube being connected to a source of variable air pressure. A certain known pressure is applied to the lower leg of the tube and transmitted to both the column of mercury and the sphygmomanometer pressure gauge and a comparison is made between the column of mercury and the dial indicia on the face of the pressure gauge to determine the accuracy of the pressure gauge. Various pressures can be applied, allowing for the determination of the accuracy of a pressure gauge throughout a range of pressures. Many sphygmomanometer users or owners do not have such a calibrating or accuracy testing device because of its size and costs. Therefore, these users or owners must return their sphygmomanometers either to the factory or a factory authorized service facility in order to have the accuracy of their sphygmomanometer checked and calibrated.
Because of the widespread use of sphygmomanometers with bellows-operated pressure gauges, the assignee of this patent application alone receives on the order of about 100 of such pressure gauges per day for testing and calibration. Thus, the need for a means by which owners and users of sphygmomanometers can easily and economically check the accuracy and calibrate their own sphygmomanometer pressure gauges is clearly present.